Femtosecond Laser Cuts into Roundworm

The team's findings give researchers an experimental system in which they will be able to investigate in great detail the genetic and molecular factors that control whether or not damaged nerves can regrow, said Chisholm, an associate professor of molecular, cell, and developmental biology at the University of California.

"This technique will enable us to find the genes that are important in allowing an axon to regenerate. In the worm, we can do systematic screening of large numbers of genes, drugs and other small molecules as well, to ask how they affect the process of regeneration," Chisholm said.

When properly focused, the energy delivered by the laser pulses breaks down chemical bonds at the targeted site, vaporizing the tissue within a tiny volume without causing side effects such as heating of surrounding tissue, Yanik said.

The duration of the laser pulses used was 200 femtoseconds, and the pulses were delivered at a rate of one thousand per second. The delicate axons severed by the procedure, with no apparent damage to surrounding tissue, were on average just 0.3 microns in diameter.

Most of the severed axons regrew within 12 to 24 hours after the laser surgery. Preliminary observations indicated that after an axon is cut, the nerve cell sprouts a new axon from the severed end that regrows to reach the target muscle. In some cases, however, it appears that the two severed ends reattach, Chisholm said.

One of the fundamental questions researchers want to answer is why nerve damage in the central nervous system - the brain and spinal cord - is usually permanent.

"In humans, peripheral nerves will regrow, but in the central nervous system the regrowth of axons is inhibited by the local environment. That's why spinal cord injuries are so serious. We want to find out why a severed axon will regrow in some situations and not in others," Chisholm said.